This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In the study of proteins, in particular for reaction intermediates, there are several cases in which spectroscopic methods such as resonance Raman, EPR, UV-vis, and MCD are unable provide a complete picture of the electronic and geometric structure of the active site. In such situations, as is the case for many non-heme iron enzymes, the use of Fe-K XAS edge and EXAFS techniques can provide crucial information. Fe K-edge analysis can resolve ambiguous oxidation states and refine metal coordination, and EXAFS can clarify ligand arrangement, bond length, and the overall coordination sphere. In order to understand how coordination environment affects electronic structure of enzymatic active sites as well as mechanistic turnover, we propose specifically to integrate XAS with our other spectroscopic techniques in order to understand the active sites of several non-heme iron enzymes, model systems, and reaction intermediates. Systems of specific interest include: tyrosine hydroxylase, halogenases, Rieske dioxygenases, intradiol dioxygenases, several {FeNO}7 analogs, model complexes of FeIV=O systems, and the binuclear iron systems of ?due ferri? polypeptides for the active site in ribonucleotide reductases.